1. Field of the Invention
The invention relates to a heating light source of a heat treatment device of the light irradiation type in which a semiconductor wafer (hereinafter called a "wafer") is heated by light for layer formation, diffusion, annealing and the like. The invention, furthermore, relates to a heating filament lamp which is used in this heating light source.
2. Description of Related Art
Heat treatment of the light irradiation type in the production of semiconductor wafers is performed in broad areas, as in layer formation, diffusion, annealing and the like.
In each of these treatments, a wafer is heated to a high temperature and treated. If a heat treatment device of the light irradiation type is used for this heat treatment, the wafer can be quickly heated. After a few seconds, the wafer temperature can increase to greater at least 1000.degree. C. Furthermore, cooling can take place quickly when the light irradiation stops.
However, when the wafer is heated, if thermal nonuniformity arises in it, a phenomenon occurs in the wafer which is called "slip" and means errors of dislocation. Here, there is the danger that scrap will be produced.
Therefore, in heat treatment of a wafer using a heat treatment device of the light irradiation type, there is a need to control the amount of light irradiation in order to uniformly increase the wafer temperature.
In a conventional lamp heating device, there are a host of halogen lamps next to one another which are electrically connected in parallel with a uniform spacing relative to one another (honeycomb). The radiance of the respective lamp is regulated. In this way, the amount of radiation emitted for the respective given zone of the wafer is controlled and the wafer is uniformly heated (conventional example 1).
In another conventional lamp heating device, there are several annular IR lamps with different diameters each, arranged concentrically, as described in Japanese patent disclosure document HEI 8-45863. The radiance of the respective zone is changed by the distance between the wafer and lamp being changed in the respective concentric zone. In this way, the wafer temperature is controlled (conventional example 2).
In the device according to conventional example 1, the filament of the respective halogen lamps located next to one another is relatively short. Since there are several such lamps connected in parallel with respect to the power source, the current flowing through the device is enormous when a given power is supplied to the lamps. Therefore, an electrical splitting cable with a large diameter must be used for large currents. Here, it is considered disadvantageous that a large device is needed.
In the device according to the conventional example 2, a light source is used in which there are several annular lamps arranged concentrically to obviate the need for a large device due to the large currents, as in the device according to the conventional example 1. Here, by changing the distance between the lamps and the wafer, the temperature uniformity is enhanced. However, in this lamp, the luminous filament does not extend uniformly in the vicinity of the insertion tubes on the ends of the arc tube. As a result, the wafer surface directly under this area has much weaker irradiance than the wafer surface directly under the filament. It has become increasingly apparent that this great difference in irradiance (difference between greater irradiance and smaller irradiance) is a significant disadvantage in that a uniform wafer surface temperature, which is essential for producing semiconductors, cannot be obtained.